In REDUCTION OF FALSE POSITIVES IN ORAL-FLUID BASED IMMUNOASSAYS U.S. patent application Ser. No 08/806,245, filed Feb. 21, 1997, (owned by the same Assignee herein) there is disclosed the use of an immuno-chromatographic strip for testing oral fluids. In a preferred embodiment, the oral fluid or oral fluid/bile salt mixture can be pretreated by passage through a chelating matrix as it passes out of the oral fluid collection device (e.g., OraQuick.RTM., Epitope, Inc., Beaverton, Oreg., USA) into the assay device (e.g., a rapid assay device such as the HIV1/2 Stat-Pak Ultra Fast HIV Assay, Chembio Diagnostic Systems, Medford, N.Y.).
In this test, and without the addition of the bile salts, it was found that mucopolysacchrides can interfere and give false positive results. It was discovered that by the addition of a bile salt, such as deoxycholate, that the false positives were reduced.
While the addition of the bile salts improved test results, these bile salts produced decreased incidence of false positives. It was found desirable to control the volume of sample released within narrower limits. Specifically, in a preferred embodiment, the bile salt is provided in an amount such that the final concentration of the bile salt in the oral fluid in the assay on the immuno-chromatographic strip ranges from about 0.1 weight percent to about 1 weight percent, more preferably from about 0.3 weight percent to about 0.6 weight percent, and most preferably from about 0.45 weight percent to about 0.55 weight percent of the solution applied to the assay. Naturally, the closer the approach of the sample to the preferred concentration, the better the overall test results.
As this example points out, the field of assaying with chromatographic strips often has needs for precise volume control. This is true, whether or not a reagent is present. Further, where a reagent is added, the reagent must be precisely controlled with respect to the volume of sample.
At the same time that precise volume control is required, it is desired that such tests be simplified to the greatest extent possible. Specifically, and because such tests are performed in large volume, it is not feasible to rely on clinical laboratory personnel to consistently meter the oral fluid relative to the provided chromatographic strip without error.
In the following description, it is to be understood that this invention will apply in any test where sample deposited on a chromatographic strip requires precise volume control. This precise volume control can be with or without pretreatment with a controlled volume of reagent, such as a salt.
It is to be understood that the chromatographic strip provides an environment that is unique as compared to many techniques looking for an analyte within a sample.
Considering the case of Daffern et al. U.S. Pat. No. 4,994,238, volume control occurs by an alternate method. In that disclosure testing for the analyte is performed on a reagent matrix layer. This reagent matrix layer has the capacity to absorb a defined volume only; by saturating the matrix layer the volume is controlled. Once the matrix layer is saturated, excess sample is allowed to overflow to a capturing absorbent layer.
The instant disclosure which follows is to be distinguished. Unlike the matrix layer with the defined volume, the chromatographic strip utilized here is not capable of self control of the volume utilized. Instead, and without volume control, the chromatographic strip here utilized can receive too little sample in which case the reagent is not properly apportioned with respect to the sample. Additionally, and where too little sample is used, the total sample and reagent may not adequately saturate the strip to give a correct indication of the analyte.
Alternately, too much sample can be delivered. In this latter case, reagent is supplied in insufficient quantity and sample is in excess quantity. Both deficiencies contribute to the likelihood of error.